isopropyl Syllabification: (i·so·pro·pyl)Pronunciation: /ˌīsəˈprōpəl/Definition of isopropyl noun [as modifier] Chemistry of or denoting the alkyl radical CH(CH3)2, derived from propane by removal of a hydrogen atom from the middle carbon atom. isopropyl in other Oxford dictionaries Definition of isopropyl in the British & World English dictionary